Core B will provide access to high-field NMR instruments and technical assistance for the individual projects. NMR spectroscopy will be used in three different ways. First, NMR spectroscopy is an efficient tool to study molecular interactions. This is based on the fact that the chemical shift is very sensitive to changes in the magnetic environment of a given spin. Differences in chemical shift between the free protein and the protein in complex with a drug, a peptide or another protein indicate, therefore, molecular interactions. The strength of NMR spectroscopy is that these molecular interactions can be detected without knowledge about the three dimensional structures of the involved molecules. Many projects described in this application will, therefore, use NMR spectroscopy to investigate if molecular interactions occur and to optimize the protein constructs for following crystallization experiments. In particular, investigations of the interaction of the thyroid hormone receptor and the estrogen receptor with different drugs and with the co-activator GRIP-1 will in this way benefit from the information provided by Core B. In the same way NMR spectroscopy will provide information about the question whether phosphorylation triggers a conformational switch in the orphan receptor SF-1. While large changes in chemical shift will indicate a major conformational switch, small local changes are indicative that phosphorylation does not change the conformation of the protein. In addition to its role as a screening tool for molecular interactions and conformational changes, NMR spectroscopy will provide information about the dynamics of nuclear receptors. In the category NMR will be used to investigate two central problems. First, the role of dynamics in the ligand binding site of the thyroid hormone and the estrogen receptor and second the function of amino acids outside of the NR boxes in GRIP-1 for specificity. Finally, NMR spectroscopy can provide structural information. If crystallization experiments do not yield diffraction-quality crystals, structure determination will be carried out by NMR spectroscopy.